Studies to date indicate that Distortion Product Otoacoustic Emissions (DPOE) responses are capable of indicating micromechanical activity of cochlear outer hair cells. Outer hair cells are essential for acute sensitivity and frequency selectivity. Therefore, the loss of outer hair cells may have an effect on the subject's ability to discriminate complex signals such as speech. The specific aim of this project is to study the effects of aging on the ability of healthy older subjects to generate DPOEs, and to correlate this measurement with the subject's ability to discriminate speech. DPOEs will be measured in two basic forms: 1) response growth or input-output functions; and 2) by plotting the frequency pattern of the DPOE amplitudes in response to constant level stimuli. Speech discrimination ability will be assessed by using the Speech. Perception in Noise (SPIN) test. Both measurements will be examined in a series of normal hearing subjects ranging in age from 20 to 70 years old. With this information, a better understanding should be obtained of: 1) the mechanisms involved in speech perception; 2) the normal aging processes occurring in the outer hair cells of the cochlea; and 3) the differentiation between changes in cochlear processes associated with normal aging and those due pathological causes.